AbstractTeratogenicity of thalidomide was demonstrated in Wistar rats following a single maternal intravenous injection during the embryonic organogenetic period. When compared to day 13 embryonic DNA isolated from untreated control mothers, differences were observed in the mean wet weights of day 13 embryos from rats treated with thalidomide during days 10 or 11 of gestation, and significantly less amounts of embryonic DNA were recovered from mothers similarly treated on days 10 or 12 of their respective gestation periods.Rat embryonic DNA may be separated into two fractions by stepwise elution from benzoylated DEAE‐cellulose (BD‐cellulose) columns with 1.0 M NaCl (SE‐DNA) and 1.8 (w/v) caffeine (CE‐DNA) solutions, respectively. Other studies using bacterial, yeast, and rat liver DNA suggested that the first fraction contains native DNA, whereas the second may exhibit some degree of single‐stranded character. Similar reproducible chromatographic profiles were obtained using a novel “batch method” developed for general application. Rat embryonic DNA was monitored by labelling in vivo with an i.p. injection of methyl‐3H‐thymidine (3H‐TdR) during days 5, 6, and 7 of the gestation period. All samples were analysed on day 13 of gestation. A simple increase in percentage of caffeine‐eluted DNA was not detected in thalidomide treated samples; however, diversity of percent () CE‐DNA within litter was noted. Briefly, the percent CE‐DNA values for embryos in one litter were ranked and arbitrarily grouped in classes with limits of mean ± 1 SD, mean ± 2 SD, and so on to generate a characteristic profile of percent CE‐DNA distribution. The number of embryos within the range of each SD unit was expressed as a percentage of each litter. A plot of the ranges of percent CE‐DNA versus percentage of each litter was used to illustrate the distribution profile of the particular litter and to be used for comparison between samples from untreated control and thalidomide and/or dimethylformamide (DMF) treated DNA. Treatment of day 12 mothers with thalidomide produced a majority of embryos having percent CE‐DNA values similar to those of untreated controls with the exception of the inclusion of a second population of embryos with much higher percent CE‐DNA values than those of the untreated controls. Similar treatment of day 11 animals produced a majority of embryos still having percent CE‐DNA values similar to those of untreated controls and also having a second group of embryos with a lower percent CE‐DNA values than those of untreated controls. Following thalidomide treatment of mothers on day 10 of gestation, although the majority of embryos had percent CE‐DNA values similar to the lowest extreme value of the untreated control, the second group of embryos had percent CE‐DNA values even lower than those of the similar respective group from 48 hour treated animal. Results from this study suggest that the teratogenic effect of thalidomide may be simply slowing down the development of certain group of cells, which are then out of synchrony with t
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